I've read that if a cowboy could even afford a revolver, then he usually couldn't afford to buy enough ammo to be proficient with it. Ammo was expensive on a cowboy salary and was fired only when really needed. Sort of like having a fire extinguisher around. You hope you don't need it but when you do it's quite handy.
Most general stores would sell ammo by the round.
Cowboy walks in an replaces the two rounds he fired at a coyote with 2 fresh ones....
